1. Field of the Invention
This invention relates to an intake port means for extracting engine exhaust gas for recirculation in a Diesel engine using exhaust gas recirculation (EGR) system.
2. Description of the Prior Art
Exhaust gas from a Diesel engine contains a large amount of soot and other minute particles, and if such soot and minute particles are recirculated together with the recirculation gas in the EGR system, various disturbances are caused by deterioration of oil or deposit of the soot. Thus, there is a need for a structure which minimizes the entry of such soot and minute particles into the EGR system at an intake port for extracting the exhaust gas. At present, Diesel engines equipped with such an EGR system in the market are relatively few, but the current trend is to apply the EGR system to Diesel engines for the purpose of purification of the exhaust gas.
In the case of gasoline engines, which are now available in the market, negative pressure at the intake side of an intake port for extracting the engine exhaust gas for EGR is large, and the EGR is effected by using such intake negative pressure, so that contrivances are made in workability and durability of the EGR system while facilitating the EGR itself, but there has not been any significant consideration from other viewpoints. Accordingly, the physical configuration of the extracting inlet for EGR is simply a hole bored on a tube wall. If the same aperture for extracting the exhaust gas for EGR as that of the conventional gasoline engine is applied to a Diesel engine, since the maximum flow rate of EGR required for the Diesel engine is large and can be comparable with the intake flow rate thereof, minute particles in the exhaust gas such as soots of the Diesel engine are apt to be recirculated back to the engine together with the exhaust gas for EGR.
In the case of a Diesel engine, the intake pressure is low, and as compared with a gasoline engine, several times more of EGR is necessary for achieving the same degree of nitrogen oxide (NOx) reduction, and hence, the extracting inlet port of the exhaust gas must be fairly large. Besides, combustion products contained in the exhaust gas, such as soots and minute particles, may cause various disturbances, e.g., deposits in the EGR system resulting in a deterioration of the function thereof, entering in engine cylinders to cause an accelerated abrasion of cylinder walls and piston rings, and an accelerated deterioration of lubricating oil.